U.S. patent application number 14/771911 was filed with the patent office on 2016-01-21 for semiconductor laser element.
The applicant listed for this patent is HAMAMATSU PHOTONICS K.K., KYOTO UNIVERSITY. Invention is credited to Kazuyoshi HIROSE, Yoshitaka KUROSAKA, Susumu NODA, Takahiro SUGIYAMA, Akiyoshi WATANABE.
Application Number | 20160020581 14/771911 |
Document ID | / |
Family ID | 51491172 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160020581 |
Kind Code |
A1 |
HIROSE; Kazuyoshi ; et
al. |
January 21, 2016 |
SEMICONDUCTOR LASER ELEMENT
Abstract
A semiconductor laser element is realized with high beam quality
(index M.sup.2<1). A diffraction grating 6ba of a diffraction
grating layer 6 extends along a principal surface 2a and is
provided on a p-side surface 6a of the diffraction grating layer 6;
the refractive index of the diffraction grating layer 6
periodically varies in directions extending along the principal
surface 2a, in the diffraction grating 6ba; the diffraction grating
6ba has a plurality of holes 6b; the plurality of holes 6b are
provided in the p-side surface 6a and arranged in translational
symmetry along a square lattice R3; the plurality of holes 6b each
have the same size and shape; each hole 6b corresponds to a lattice
point of the diffraction grating 6ba and is of a triangular prism
shape; a shape of a bottom face 6c of the hole 6b is an approximate
right triangle.
Inventors: |
HIROSE; Kazuyoshi;
(Hamamatsu-shi, JP) ; WATANABE; Akiyoshi;
(Hamamatsu-shi, JP) ; KUROSAKA; Yoshitaka;
(Hamamatsu-shi, JP) ; SUGIYAMA; Takahiro;
(Hamamatsu-shi, JP) ; NODA; Susumu; (Kyoto-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYOTO UNIVERSITY
HAMAMATSU PHOTONICS K.K. |
Kyoto-shi, Kyoto
Hamamatsu-shi, Shizuoka |
|
JP
JP |
|
|
Family ID: |
51491172 |
Appl. No.: |
14/771911 |
Filed: |
February 27, 2014 |
PCT Filed: |
February 27, 2014 |
PCT NO: |
PCT/JP2014/054916 |
371 Date: |
September 1, 2015 |
Current U.S.
Class: |
372/46.01 ;
372/50.11 |
Current CPC
Class: |
H01S 5/18319 20130101;
H01S 5/105 20130101; H01S 5/18 20130101; H01S 3/08009 20130101;
H01S 2301/14 20130101; H01S 5/183 20130101; H01S 5/187 20130101;
H01S 5/12 20130101; H01S 5/04256 20190801; H01S 5/1231 20130101;
H01S 5/04254 20190801 |
International
Class: |
H01S 5/18 20060101
H01S005/18; H01S 5/10 20060101 H01S005/10; H01S 5/12 20060101
H01S005/12; H01S 5/042 20060101 H01S005/042 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2013 |
JP |
2013-041973 |
Sep 27, 2013 |
JP |
2013-202086 |
Claims
1. A semiconductor laser element comprising a semiconductor
laminate, wherein the semiconductor laminate comprises a support
substrate, a first cladding layer, an active layer, a diffraction
grating layer, and a second cladding layer, wherein the first
cladding layer, the active layer, the diffraction grating layer,
and the second cladding layer are provided on a principal surface
of the support substrate, wherein the active layer and the
diffraction grating layer are provided between the first cladding
layer and the second cladding layer, wherein the active layer
generates light, wherein the second cladding layer has a
conductivity type different from a conductivity type of the first
cladding layer, wherein the diffraction grating layer has a
diffraction grating, wherein the diffraction grating has a
two-dimensional photonic crystal structure of square lattice
arrangement, wherein the two-dimensional photonic crystal structure
has a plurality of holes and extends along the principal surface,
wherein the plurality of holes have an identical shape and are
arranged along a square lattice of the diffraction grating, wherein
the hole corresponds to a lattice point of the diffraction grating,
wherein a shape of a bottom face of the hole is an approximate
right triangle, wherein the hole has a refractive index different
from a refractive index of a base material of the diffraction
grating, wherein a node of an electromagnetic field generated in
the diffraction grating by luminescence of the active layer is
located substantially at the same position as a centroid of the
approximate right triangle of the hole, and wherein an extremum of
intensity of a magnetic field in the electromagnetic field is
present around the hole.
2. The semiconductor laser element according to claim 1, wherein
the semiconductor laminate further comprises an electron blocking
layer, and wherein the electron blocking layer lies between a layer
with a conductivity type of p-type in the first cladding layer and
the second cladding layer, and the active layer.
3. The semiconductor laser element according to claim 1, wherein
the diffraction grating layer lies between a layer with a
conductivity type of p-type in the first cladding layer and the
second cladding layer, and the active layer.
4. The semiconductor laser element according to claim 1, wherein a
material of the semiconductor laminate is a III-V semiconductor
containing GaAs.
5. The semiconductor laser element according to claim 1, wherein
the bottom face has a first side and a second side, wherein the
first side and the second side make a right angle, and wherein the
first side is inclined relative to a lattice vector of a square
lattice.
6. The semiconductor laser element according to claim 1, wherein
each of three vertices of the approximate right triangle of the
bottom face is rounded so as to overlap a circumference of a
reference circle touching the sides internally at the vertex.
7. The semiconductor laser element according to claim 1, wherein
the approximate right triangle of the bottom face has a first side
and a second side, wherein the first side and the second side make
a right angle, wherein each of three vertices of the approximate
right triangle of the bottom face is rounded so as to overlap a
circumference of a reference circle touching the sides internally
at the vertex, wherein the shape of the approximate right triangle
of the hole satisfies any one of the following conditions (1) to
(10): (1) a roundedness is 0.00.times.a lattice constant, a filling
factor is not less than 10% and not more than 25%, and an aspect
ratio is not less than 1.00 and not more than 1.16; (2) a
roundedness is 0.00.times.a lattice constant, a filling factor is
not less than 15% and not more than 25%, and an aspect ratio is not
less than 1.16 and not more than 1.20; (3) a roundedness is
0.05.times.a lattice constant, a filling factor is not less than 9%
and not more than 24%, and an aspect ratio is not less than 1.00
and not more than 1.20; (4) a roundedness is 0.10.times.a lattice
constant, a filling factor is not less than 10% and not more than
22%, and an aspect ratio is not less than 1.00 and not more than
1.08; (5) a roundedness is 0.10.times.a lattice constant, a filling
factor is not less than 10% and not more than 21%, and an aspect
ratio is not less than 1.08 and not more than 1.12; (6) a
roundedness is 0.10.times.a lattice constant, a filling factor is
not less than 10% and not more than 18%, and an aspect ratio is not
less than 1.12 and not more than 1.20; (7) a roundedness is
0.15.times.a lattice constant, a filling factor is not less than
11% and not more than 22%, and an aspect ratio is not less than
1.00 and not more than 1.08; (8) a roundedness is 0.15.times.a
lattice constant, a filling factor is not less than 11% and not
more than 21%, and an aspect ratio is not less than 1.08 and not
more than 1.16; (9) a roundedness is 0.15.times.a lattice constant,
a filling factor is not less than 11% and not more than 20%, and an
aspect ratio is not less than 1.16 and not more than 1.20; (10) a
roundedness is 0.20.times.a lattice constant, a filling factor is
not less than 13% and not more than 22%, and an aspect ratio is not
less than 1.00 and not more than 1.20, wherein the roundedness is a
radius of the reference circle, wherein the lattice constant is a
length of one side of a unit lattice of the diffraction grating,
wherein the filling factor is a rate of an area of the approximate
right triangle of the hole to an area of the unit lattice, and
wherein the aspect ratio is a ratio of a side length of the first
side and a side length of the second side on the assumption that
the vertices are not rounded.
Description
TECHNICAL FIELD
[0001] The present invention relates to a semiconductor laser
element with a photonic crystal structure.
BACKGROUND ART
[0002] Patent Literature 1 discloses a two-dimensional photonic
crystal vertical cavity surface emitting laser. Its lattice
structure is a square lattice or orthogonal lattice. The lattice
structure has translational symmetry. The shape of lattice points
is triangular.
[0003] Patent Literature 2 discloses a surface emitting laser. The
surface emitting laser has a laminated body, a first electrode, and
a second electrode. The laminated body has an active layer and a
two-dimensional photonic crystal. The laminated body lies between
the first electrode and the second electrode. The first electrode
has an annular shape. The two-dimensional photonic crystal lases to
emit a laser beam. The laser beam has an annular cross-sectional
shape and is radially polarized.
CITATION LIST
Patent Literatures
[0004] Patent Literature 1: Japanese Patent Application Laid-open
Publication No. 2004-296538 [0005] Patent Literature 2: Japanese
Patent Application Laid-open Publication No. 2007-258261
Non Patent Literatures
[0005] [0006] Non Patent Literature 1: Y. Liang et al.,
"Three-dimensional coupled-wave model for square-lattice photonic
crystal lasers with transverse electric polarization: A general
approach," Phys. Rev. B84, 195119 (2011) [0007] Non Patent
Literature 2: Chao Peng et al., "Coupled-wave analysis for
photonic-crystal surface-emitting lasers on air holes with
arbitrary sidewalls," Optics Express Vol. 19 No. 24, pp.
24672-24686 (2011) [0008] Non Patent Literature 3: Y. Kurosaka et
al., "Controlling vertical optical confinement in two-dimensional
surface-emitting photonic-crystal lasers by shape of air holes,"
Opt. Express 16, 18485-18494 (2008)
SUMMARY OF INVENTION
Technical Problem
[0009] The semiconductor lasers have been used heretofore in
various fields, e.g., communications, processing, measurement,
excitation, wavelength conversion, and so on. However, since the
conventional semiconductor lasers have the problems of low beam
quality and poor concentration characteristics, their usage is
limited and thus lasers with good beam quality such as solid-state
lasers, gas lasers, and fiber lasers are mainly used in
high-precision microfabrication and advanced optical fields. On the
other hand, the semiconductor lasers have characteristics of
smaller size and higher efficiency than the other lasers. An object
of the present invention, in view of the above circumstances, is to
realize a semiconductor laser element with high beam quality (index
M.sup.2<1).
Solution to Problem
[0010] A semiconductor laser element according to one aspect of the
present invention comprises a semiconductor laminate, wherein the
semiconductor laminate comprises a support substrate, a first
cladding layer, an active layer, a diffraction grating layer, and a
second cladding layer, wherein the first cladding layer, the active
layer, the diffraction grating layer, and the second cladding layer
are provided on a principal surface of the support substrate,
wherein the active layer and the diffraction grating layer are
provided between the first cladding layer and the second cladding
layer, wherein the active layer generates light, wherein the second
cladding layer has a conductivity type different from a
conductivity type of the first cladding layer, wherein the
diffraction grating layer has a diffraction grating, wherein the
diffraction grating has a two-dimensional photonic crystal
structure of square lattice arrangement, wherein the
two-dimensional photonic crystal structure has a plurality of holes
and extends along the principal surface, wherein the plurality of
holes have an identical shape and are arranged along a square
lattice of the diffraction grating, wherein the hole corresponds to
a lattice point of the diffraction grating, wherein a shape of a
bottom face of the hole is an approximate right triangle, wherein
the hole has a refractive index different from a refractive index
of a base material of the diffraction grating, wherein a node of an
electromagnetic field generated in the diffraction grating by
luminescence of the active layer is located substantially at the
same position as a centroid of the approximate right triangle of
the hole, and wherein an extremum of intensity of a magnetic field
in the electromagnetic field is present around the hole. The
semiconductor laser element according to the one aspect of the
present invention outputs the laser beam through the diffraction
grating and this diffraction grating has a plurality of lattice
points of the approximate right triangle arranged along the square
lattice. In the case of the electromagnetic field mode at the
second band edge from the low frequency side near the second
.GAMMA. point of the square lattice (or in the case of Mode B), the
node of the electromagnetic field generated in the diffraction
grating by luminescence of the active layer is located
substantially at the same position as the centroid of the
approximate right triangle of the hole, and the extremum of
intensity of the magnetic field in the electromagnetic field on the
square lattice is present around the hole. It was discovered by
Inventor's intensive and extensive research that the beam quality
of index M.sup.2<1 could be realized in this case of Mode B.
Therefore, the laser beam output by the semiconductor laser element
according to the one aspect of the present invention has the beam
quality of the index M.sup.2<1.
[0011] In the semiconductor laser element according to the one
aspect of the present invention, the semiconductor laminate further
comprises an electron blocking layer, and the electron blocking
layer lies between a layer with a conductivity type of p-type in
the first cladding layer and the second cladding layer, and the
active layer. The electron blocking layer enables capability for
high output.
[0012] In the semiconductor laser element according to the one
aspect of the present invention, the diffraction grating layer lies
between a layer with a conductivity type of p-type in the first
cladding layer and the second cladding layer, and the active layer.
When the semiconductor laminate is formed from the n-side layer,
the diffraction grating layer is formed after formation of the
active layer and thus the active layer is prevented from being
directly damaged during processing of the diffraction grating
layer, whereby degradation of the active layer can be avoided.
[0013] In the semiconductor laser element according to the one
aspect of the present invention, the bottom face has a first side
and a second side, the first side and the second side make a right
angle, and the first side is inclined relative to a lattice vector
of the square lattice. Since oscillation at the band edge B is
possible even with the inclination of the approximate right
triangle of the lattice point relative to the lattice vector, the
beam quality of the index M.sup.2 can be maintained, which was
discovered by Inventor's intensive and extensive research. In the
steps of manufacturing the semiconductor laser element, when the
diffraction grating layer and the laminate subsequent thereto are
formed by regrowth in the MOCVD (Metal Organic Chemical Vapor
Deposition) process, the quality of the laminate can be optimized
by the foregoing inclination, depending upon the shape of the
lattice point.
[0014] In the semiconductor laser element according to the one
aspect of the present invention, a material of the semiconductor
laminate is a III-V semiconductor containing GaAs. In this manner,
the semiconductor laminate of the semiconductor laser element
according to the one aspect of the present invention can be
manufactured using the III-V semiconductor containing GaAs. Since
the manufacturing technology has been established for such material
system, manufacture of the semiconductor laser element becomes
relatively easier.
[0015] In the semiconductor laser element according to the one
aspect of the present invention, each of three vertices of the
approximate right triangle of the bottom face is rounded so as to
overlap a circumference of a reference circle touching the sides
internally at the vertex. It was discovered by Inventor's intensive
and extensive research that the beam quality of the index M.sup.2
could be maintained even if the three vertices of the approximate
right triangle of the lattice point were rounded.
[0016] In the semiconductor laser element according to the one
aspect of the present invention, the approximate right triangle of
the bottom face has a first side and a second side; the first side
and the second side make a right angle; each of three vertices of
the approximate right triangle of the bottom face is rounded so as
to overlap a circumference of a reference circle touching the sides
internally at the vertex; the shape of the approximate right
triangle of the hole satisfies any one of the following conditions
(1) to (10): (1) a roundedness is 0.00.times.a lattice constant, a
filling factor is not less than 10% and not more than 25%, and an
aspect ratio is not less than 1.00 and not more than 1.16; (2) a
roundedness is 0.00.times.a lattice constant, a filling factor is
not less than 15% and not more than 25%, and an aspect ratio is not
less than 1.16 and not more than 1.20; (3) a roundedness is
0.05.times.a lattice constant, a filling factor is not less than 9%
and not more than 24%, and an aspect ratio is not less than 1.00
and not more than 1.20; (4) a roundedness is 0.10.times.a lattice
constant, a filling factor is not less than 10% and not more than
22%, and an aspect ratio is not less than 1.00 and not more than
1.08; (5) a roundedness is 0.10.times.a lattice constant, a filling
factor is not less than 10% and not more than 21%, and an aspect
ratio is not less than 1.08 and not more than 1.12; (6) a
roundedness is 0.10.times.a lattice constant, a filling factor is
not less than 10% and not more than 18%, and an aspect ratio is not
less than 1.12 and not more than 1.20; (7) a roundedness is
0.15.times.a lattice constant, a filling factor is not less than
11% and not more than 22%, and an aspect ratio is not less than
1.00 and not more than 1.08; (8) a roundedness is 0.15.times.a
lattice constant, a filling factor is not less than 11% and not
more than 21%, and an aspect ratio is not less than 1.08 and not
more than 1.16; (9) a roundedness is 0.15.times.a lattice constant,
a filling factor is not less than 11% and not more than 20%, and an
aspect ratio is not less than 1.16 and not more than 1.20; (10) a
roundedness is 0.20.times.a lattice constant, a filling factor is
not less than 13% and not more than 22%, and an aspect ratio is not
less than 1.00 and not more than 1.20; where the roundedness is a
radius of the reference circle, the lattice constant is a length of
one side of a unit lattice of the diffraction grating, the filling
factor is a rate of an area of the approximate right triangle of
the hole to an area of the unit lattice, and the aspect ratio is a
ratio of a side length of the first side and a side length of the
second side on the assumption that the vertices are not rounded.
When the shape of the approximate right triangle of the bottom face
of the hole satisfies any one of the foregoing conditions (1) to
(10), the oscillation in Mode B becomes particularly prominent,
which was discovered by the Inventor.
Advantageous Effect of Invention
[0017] According to one aspect of the present invention, the
semiconductor laser element can be realized with high beam quality
(index M.sup.2<1).
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a drawing for explaining a configuration of a
semiconductor laser element according to an embodiment.
[0019] FIG. 2 is a drawing for explaining a configuration of a
square lattice according to the embodiment.
[0020] FIG. 3 is a drawing for explaining a configuration of a
lattice point of the square lattice according to the
embodiment.
[0021] FIG. 4 is a drawing for explaining the beam quality of the
semiconductor laser element according to the embodiment.
[0022] FIG. 5 is a drawing for explaining electromagnetic fields
generated by a diffraction grating according to the embodiment.
[0023] FIG. 6 is a drawing for explaining magnetic field
distributions and radiation coefficients in respective modes at
four band edges, in an example of the lattice point shape of the
diffraction grating according to the embodiment.
[0024] FIG. 7 is a drawing for explaining the configuration of the
lattice point of the square lattice according to the
embodiment.
[0025] FIG. 8 is a drawing for explaining the configuration of the
lattice point of the square lattice according to the
embodiment.
[0026] FIG. 9 is a drawing for explaining the configuration of the
lattice point of the square lattice according to the
embodiment.
[0027] FIG. 10 is a drawing for explaining the configuration of the
lattice point of the square lattice according to the
embodiment.
[0028] FIG. 11 is a drawing for explaining the configuration of the
lattice point of the square lattice according to the
embodiment.
[0029] FIG. 12 is a drawing for explaining the configuration of the
lattice point of the square lattice according to the
embodiment.
[0030] FIG. 13 is a drawing for explaining a method for
manufacturing the semiconductor laser element according to the
embodiment.
[0031] FIG. 14 is a drawing for explaining the structure of the
semiconductor laser element according to the embodiment.
[0032] FIG. 15 is a drawing for explaining the beam quality of the
semiconductor laser element according to the embodiment.
[0033] FIG. 16 is a drawing for explaining the beam quality of the
semiconductor laser element according to the embodiment.
[0034] FIG. 17 is a drawing for explaining the beam quality of the
semiconductor laser element according to the embodiment.
[0035] FIG. 18 is a drawing for explaining that a laser beam is
oscillated at band edge B in the semiconductor laser element
according to the embodiment.
[0036] FIG. 19 is a drawing illustrating polarization angle
dependence of the laser beam of the semiconductor laser element
according to the embodiment, and drawing for explaining that
contribution of Mode B to oscillated electromagnetic field modes is
significant.
[0037] FIG. 20 is a drawing for illustrating the polarization angle
dependence of the laser beam of the semiconductor laser element
according to the embodiment, and drawing for explaining that the
contribution of Mode B to oscillated electromagnetic field modes is
significant.
[0038] FIG. 21 is a drawing for explaining an oscillation spectrum
at an injected current of 500 mA, in the semiconductor laser
element according to the embodiment.
[0039] FIG. 22 is SEM images of an example of the semiconductor
laser element according to the embodiment.
[0040] FIG. 23 is a drawing showing specific examples of the shape
of the unit lattice.
[0041] FIG. 24 is a drawing showing correlations between radiation
coefficient and filling factor in each of four types of
electromagnetic field modes.
[0042] FIG. 25 is a drawing showing the simulation result of
threshold gain difference between Mode A and Mode B.
[0043] FIG. 26 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0044] FIG. 27 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0045] FIG. 28 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0046] FIG. 29 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0047] FIG. 30 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0048] FIG. 31 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0049] FIG. 32 is a drawing showing a con-elation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0050] FIG. 33 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0051] FIG. 34 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0052] FIG. 35 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0053] FIG. 36 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
roundedness with the aspect ratio kept constant.
[0054] FIG. 37 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
aspect ratio with the roundedness kept constant.
[0055] FIG. 38 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
aspect ratio with the roundedness kept constant.
[0056] FIG. 39 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
aspect ratio with the roundedness kept constant.
[0057] FIG. 40 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
aspect ratio with the roundedness kept constant.
[0058] FIG. 41 is a drawing showing a correlation of threshold gain
differences with values of the filling factor and values of the
aspect ratio with the roundedness kept constant.
DESCRIPTION OF EMBODIMENTS
[0059] Embodiments of the present invention will be described below
in detail with reference to the drawings. In the description of the
drawings the same elements will be denoted by the same reference
signs as much as possible, without redundant description. Referring
to FIG. 1, the configuration of the semiconductor laser element 1
according to an embodiment will be described. An orthogonal
coordinate system composed of x-axis, y-axis, and z-axis is shown
in FIG. 1. The arrangement of the x-axis, y-axis, z-axis, and the
semiconductor laser element (particularly, diffraction grating 6ba
and holes 6b) shall be the same in FIGS. 1-6, 15-20, and 22. The
semiconductor laser element 1 is a regrowth type PCSEL (Photonic
Crystal Surface Emitting Laser).
[0060] The semiconductor laser element 1 has a semiconductor
laminate 1a, an AR coat 9a (Anti Reflective: non-reflective), an
n-side electrode 9, and a p-side electrode 10. Materials of the
semiconductor laminate 1a are, for example, III-V semiconductors
containing GaAs. The semiconductor laminate 1a has a support
substrate 2, a laminate 1b1, a diffraction grating layer 6, and a
laminate 1b2. The laminate 1b1 has an n-type cladding layer 3, an
active layer 4, and an electron blocking layer 5. The laminate 1b2
has a p-type cladding layer 7 and a contact layer 8. The laminate
1b1 is provided on a principal surface 2a of the support substrate
2. The laminate 1b2 is provided on the diffraction grating layer 6.
The diffraction grating layer 6 is provided between the laminate
1b1 and the laminate 1b2. The n-side electrode 9 is provided on a
back surface 1a2 of the semiconductor laminate 1a. The back surface
1a2 lies on the opposite side to a front surface 1a1, is a face on
the opposite side to the principal surface 2a, and corresponds to a
back surface of the support substrate 2. The n-side electrode 9 is
in contact with the back surface 1a2. The n-side electrode 9 has
such a shape as to surround an opening 9b. The n-side electrode 9
defines the opening 9b. The opening 9b includes a central region of
the back surface 1a2. The AR coat 9a is provided on the back
surface 1a2. The AR coat 9a, when viewed on a plan view, is
provided on regions except for the n-side electrode 9 in the back
surface 1a2. The AR coat 9a is in contact with the back surface
1a2. The p-side electrode 10 is provided on the front surface 1a1
of the semiconductor laminate 1a (front surface of the contact
layer 8) lying on the side indicated by a direction R1. When a
voltage is applied between the n-side electrode 9 and the p-side
electrode 10 to allow an electric current to flow through the
semiconductor laminate 1a, a laser beam L1 is output in the z-axis
direction.
[0061] The n-type cladding layer 3, active layer 4, electron
blocking layer 5, diffraction grating layer 6, p-type cladding
layer 7, and contact layer 8 are stacked in order in the opposite
direction to the z-axis direction (or in a direction of a normal
vector to the principal surface 2a) from the principal surface 2a
by epitaxial growth. The n-type cladding layer 3, active layer 4,
diffraction grating layer 6, and p-type cladding layer 7 are
provided on the principal surface 2a. The active layer 4 and the
diffraction grating layer 6 are provided between the n-type
cladding layer 3 and the p-type cladding layer 7. The support
substrate 2, n-type cladding layer 3, active layer 4, electron
blocking layer 5, diffraction grating layer 6, p-type cladding
layer 7, and contact layer 8 extend along the xy plane. The back
surface 1a2, principal surface 2a, p-side surface 6a of the
diffraction grating layer 6, and front surface 1a1 (the front
surface of the contact layer 8) extend along the xy plane.
[0062] The diffraction grating layer 6 has a diffraction grating
6ba. The diffraction grating 6ba has a two-dimensional photonic
crystal structure of square lattice arrangement. The
two-dimensional photonic crystal structure of the diffraction
grating 6ba extends along the principal surface 2a. The
two-dimensional photonic crystal structure of the diffraction
grating 6ba is a crystal structure in two dimensions (xy plane).
The diffraction grating 6ba is provided on the p-side surface 6a of
the diffraction grating layer 6. The refractive index of the
diffraction grating layer 6 periodically varies in directions
extending along the principal surface 2a (the x-axis direction and
y-axis direction), in the diffraction grating 6ba. The
two-dimensional photonic crystal structure of the diffraction
grating 6ba has a plurality of holes 6b. The plurality of holes 6b
have an identical shape (approximate triangular prism shape). The
plurality of holes 6b are periodically arranged in the directions
extending along the principal surface 2a (the x-axis direction and
y-axis direction), in a base material of the diffraction grating
6ba. Namely, the plurality of holes 6b are arranged along the
square lattice of the diffraction grating 6ba. Each hole 6b
corresponds to a lattice point of the diffraction grating 6ba. The
holes 6b have the refractive index different from that of the base
material of the diffraction grating 6ba. The plurality of holes 6b
cause the refractive index of the diffraction grating 6ba to
periodically vary in the directions extending along the principal
surface 2a (the x-axis direction and y-axis direction), for light
of the same wavelength. The holes 6b are of the approximate
triangular prism shape. This approximate triangular prism shape
extends from a bottom face 6c of the hole 6b in the p-side surface
6a toward the p-side. The shape of the bottom face 6c of the hole
6b and the shape of the opening of the hole 6b (the opening of the
hole 6b in the p-side surface 6a) have the same shape and the both
are an approximate right triangle. It is noted herein that the
shape allows of deformation made in a manufacturing process.
[0063] A material of the support substrate 2 is, for example,
n-type GaAs. A material of the n-type cladding layer 3 is, for
example, n-type AlGaAs. The thickness of the n-type cladding layer
3 is, for example, about 2000 nm. For example, when the oscillation
wavelength is assumed to be 980 nm, the refractive index of the
n-type cladding layer 3 is about 3.11.
[0064] The active layer 4 generates light. The active layer 4 has,
for example, three quantum well layers. A material of the quantum
well layers of the active layer 4 is, for example, i-type InGaAs. A
material of barrier layers of the active layer 4 is, for example,
i-type AlGaAs. The active layer 4 can have a guide layer in contact
with the n-type cladding layer 3. A material of this guide layer of
the active layer 4 is, for example, i-type AlGaAs. The thickness of
the active layer 4 is, for example, about 140 nm. The refractive
index of the active layer 4 is about 3.49, for example, when it is
assumed that the oscillation wavelength is equal to 980 nm.
[0065] The electron blocking layer 5 lies between the p-type
cladding layer 7 with the conductivity type of p-type and the
active layer 4. A material of the electron blocking layer 5 is, for
example, i-type AlGaAs. The electron blocking layer 5 can have a
guide layer in contact with the diffraction grating layer 6. A
material of this guide layer of the electron blocking layer 5 is,
for example, i-type AlGaAs. The thickness of the electron blocking
layer 5 is, for example, about 35 nm. The refractive index of the
electron blocking layer 5 is about 3.33, for example, when it is
assumed that the oscillation wavelength is equal to 980 nm.
[0066] The diffraction grating layer 6 lies between the p-type
cladding layer 7 with the conductivity type of p-type and the
active layer 4. The diffraction grating layer 6 has the diffraction
grating 6ba of the two-dimensional photonic crystal structure. The
diffraction grating layer 6 further has a guide layer in contact
with the electron blocking layer 5. The thickness of the
diffraction grating layer 6 is, for example, about 300 nm. A
material of the guide layer of the diffraction grating layer 6 is,
for example, i-type GaAs. The base material of the diffraction
grating layer 6ba is, for example, i-type GaAs, i-type AlGaAs, or
the like. The diffraction grating 6ba has the plurality of holes 6b
(hollow spaces). The plurality of holes 6b are periodically
provided in the x-axis direction and y-axis direction, in the base
material of the diffraction grating 6ba. Because of the plurality
of holes 6b, the refractive index of the diffraction grating 6ba
periodically varies in the directions extending along the principal
surface 2a (or in the x-axis direction and y-axis direction), for
light of the same wavelength. The refractive index of the
diffraction grating 6ba can be estimated, for example, as follows:
the oscillation wavelength is assumed to be 980 nm, the holes 6b
are assumed to be hollow spaces with the refractive index=1, and
dielectric constants of respective portions (squares of refractive
indices herein) are averaged depending upon the area of the holes
6b to the surface of the diffraction grating 6ba (the surface
extending along the xy plane), to obtain a value of dielectric
constant to define the refractive index. The depth of the holes 6b
is, for example, 200 nm. If the thickness of the diffraction
grating layer 6 is about 300 nm and the depth of the holes 6b is
300 nm, the diffraction grating layer 6 has no guide layer. The
laser beam L1 is emitted mainly from a luminous region R2.
[0067] A material of the p-type cladding layer 7 is, for example,
p-type AlGaAs. The thickness of the p-type cladding layer 7 is, for
example, about 2000 nm. The refractive index of the p-type cladding
layer 7 is about 3.27, for example, when the oscillation wavelength
is assumed to be 980 nm. The conductivity type of the p-type
cladding layer 7 and the conductivity type of the n-type cladding
layer 3 are different from each other.
[0068] A material of the contact layer 8 is, for example, p-type
GaAs. The thickness of the contact layer 8 is, for example, about
200 nm. The refractive index of the contact layer 8 is about 3.52,
for example, when the oscillation wavelength is assumed to be 980
nm.
[0069] A material of the n-side electrode 9 to be used herein can
be a material for electrodes provided on semiconductor layers of
GaAs-based materials. The material of the n-side electrode 9, can
be, for example, a mixture of a metal such as Au with a
semiconductor such as Ge. The n-side electrode can be, for example,
AuGe, AuGe/Au, or the like.
[0070] A material of the p-side electrode 10 to be used herein can
be a material for the electrodes provided on the semiconductor
layers of GaAs-based materials. The material of the p-side
electrode 10 can be, for example, a metal such as Au, Ti, Pt, or
Cr. The p-side electrode 10 can be, for example, Ti/Pt/Au, Ti/Au,
Cr/Au, or the like, in order from the GaAs semiconductor layer
side. The contact layer 8 in contact with the p-side electrode 10
is doped with an impurity in a high concentration of not less than
1.times.10.sup.19/cm.sup.-3. The shape of the surface of the p-side
electrode 10 is, for example, square and the area of the shape of
this surface of the p-side electrode 10 is 200.times.200
.mu.m.sup.2.
[0071] The configuration of the diffraction grating 6ba will be
described with reference to FIG. 2. FIG. 2 is a drawing of the
diffraction grating 6ba viewed from the side where the principal
surface 2a lies. The shape of the holes 6b shown in FIG. 2 is the
shape of the bottom faces 6c of the holes 6b (cross sections of the
holes 6b in the xy plane) and is the same as the shape of the
openings of the holes 6b in the p-side surface 6a. The plurality of
holes 6b are provided in the p-side surface 6a. The plurality of
holes 6b each have the same shape. The hole 6b corresponds to a
lattice point of the diffraction grating 6ba. The shape of the
bottom face 6c of the hole 6b (which is a cross section of the hole
6b in the xy plane, or the opening of the hole 6b in the p-side
surface 6a) is an approximate right triangle as shown in FIG. 3.
The plurality of holes 6b are arranged in translational symmetry
along a virtual square lattice R3. The square lattice R3 consists
of a plurality of virtual unit lattices R3a. The square lattice R3
is defined by lattice vector VX and lattice vector VY. The
plurality of unit lattices R3a are continuously arranged in a
direction defined by the lattice vector VX and in a direction
defined by the lattice vector VY. The direction of the lattice
vector VX is identical with the x-axis direction. The direction of
the lattice vector VY is identical with the y-axis direction.
[0072] The configuration of the lattice point (hole 6b) of the
diffraction grating layer 6 will be described with reference to
FIG. 3. One unit lattice R3a has one hole 6b. The unit lattice R3a
is square. The lattice constant of the square lattice R3 (length of
one side of the unit lattice R3a), when a value of the lattice
constant is a, is, for example, a=approximately 290 nm. The shape
of the hole 6b shown in FIG. 3 is the shape of the bottom face 6c
of the hole 6b and is the same as the shape of the opening of the
hole 6b in the p-side surface 6a. The bottom face 6c of the hole 6b
has a first side 6b1, a second side 6b2, and a third side 6b3. The
third side 6b3 corresponds to the hypotenuse of the approximate
right triangle of the bottom face 6c of the hole 6b. The first side
6b1 and the second side 6b2 make a right angle.
[0073] An angle .PHI. between the first side 6b1 and the lattice
vector VX (angle .PHI. between the second side 6b2 and the lattice
vector VY) is approximately 0.degree. in the present embodiment.
The angle .PHI. can be any angle. In viewing the xy plane including
the hole 6b from the z-axis direction, when the downward view from
the +z-direction is compared with the upward view from the
-z-direction, the viewed shapes of the hole 6b look mirror-inverted
from each other, in any direction on the xy plane, but they are the
same structure. For this reason, the same effect is achieved with
approximate right triangle shapes obtained by mirror inversion of
the approximate right triangle of the hole 6b in the xy plane with
respect to the x-axis direction or the y-axis direction or the both
directions or the like. When the angle .PHI. is larger than
0.degree., the first side 6b1 is inclined relative to the lattice
vector VX and the second side 6b2 is inclined relative to the
lattice vector VY.
[0074] Each of the vertex 6b4, vertex 6b5, and vertex 6b6 of the
approximate right triangle of the bottom face 6c of the hole 6b is
rounded so as to overlap the circumference of a reference circle
Ci. The reference circle Ci touches the sides internally at each of
the vertex 6b4, vertex 6b5, and vertex 6b6. Roundedness K1 of the
vertex 6b4, vertex 6b5, and vertex 6b6 is represented by a
reference radius Ra of the reference circle Ci. When the value of
the lattice constant a is represented by a, K1 is equal to
k.times.a (where a is the lattice constant). In the present
embodiment K1 is approximately 0.10.times.a. K1 can be in the range
of not less than 0.00.times.a and not more than 0.25.times.a.
[0075] When the shape of the bottom face 6c of the hole 6b is
assumed to be a right triangle without roundedness of the vertices,
the length of a side including the first side 6b1 is defined as
side length b and the length of a side including the second side
6b2 as side length h. A value K2 obtained by dividing the side
length h by the side length b (aspect ratio) is K2=h/b, where h is
a value of the side length h and b is a value of the side length b.
In the present embodiment K2 is 1.0. K2 can be not less than 1.0
and not more than 2.0.
[0076] A filling factor K3 of the bottom face 6c of the hole 6b is
a rate (%) of the area of the bottom face 6c of the hole 6b to the
area of the unit lattice R3a. In the present embodiment K3 is 10%.
K3 can be not more than 35%.
[0077] The beam quality of the semiconductor laser element 1 will
be described with reference to FIG. 4. The semiconductor laser
element 1 outputs the laser beam L1 in the z-axis direction. The
laser beam L1 travels through a lens L2 to be concentrated at a
beam waist R4. A beam shape R5 is a beam shape of a standard
Gaussian beam. A beam shape R6 is a beam shape of the laser beam L1
from the semiconductor laser element 1. A beam divergence angle
.theta. of the beam shape R5 is larger than a beam divergence angle
.THETA. of the beam shape R6. A converging radius d of the beam
shape R5 is larger than a converging radius D of the beam shape R6.
The converging radius is a value of the beam radius W at the beam
waist R4.
[0078] A value obtained by dividing the product of the converging
radius D and the beam divergence angle .THETA. by the product of
the converging radius d and the beam divergence angle .theta. is a
value of index M.sup.2 and indicates the beam quality. When the
value of index M.sup.2 is represented by M.sup.2, the relation of
D.THETA.=M.sup.2d.theta. holds. For the standard Gaussian beam, the
index M.sup.2=1. When a laser beam has the index M.sup.2>1, the
beam quality of this laser beam is lower than that of the standard
Gaussian beam. When a laser beam has the index M.sup.2<1, the
beam quality of this laser beam is higher than that of the standard
Gaussian beam. In the case of the semiconductor laser element 1, as
shown in FIG. 4, the index M.sup.2<1. Namely, the beam quality
of the laser beam of the semiconductor laser element 1 is higher
than that of the standard Gaussian beam.
[0079] Modes of electromagnetic fields generated by the diffraction
grating 6ba will be described with reference to FIG. 5. The modes
of electromagnetic fields generated by the diffraction grating 6ba
include four modes near the second .GAMMA. point of the square
lattice, which are Mode A, Mode B, Mode C, and Mode D shown in part
(A) of FIG. 5, part (B) of FIG. 5, part (C) of FIG. 5, and part (D)
of FIG. 5, respectively. Each of parts (A) to (D) of FIG. 5 shows
the hole 6b arranged in the unit lattice R3a, directions R7 of the
electric field in the unit lattice R3a, and a magnetic field
distribution M1 in the unit lattice R3a. The magnetic field
distribution M1 shows approximately circular regions with
relatively high intensity of the magnetic field included in the
electromagnetic field generated in the diffraction grating 6ba by
luminescence of the active layer 4, and includes extrema of
intensity of the magnetic field. In the laser beam L1 of the
semiconductor laser element 1, components generated by the
electromagnetic field in Mode B are larger than components
generated by the respective electromagnetic fields in Mode A, Mode
C, and Mode D. In the case of Mode B, a node R8 of the
electromagnetic field is located at a position approximately
identical with the centroid of the approximate right triangle of
the hole 6b (the shape of the bottom face 6c). In the case of Mode
B, the magnetic field distribution M1 (the extrema of intensity of
the magnetic field in the electromagnetic field generated in the
diffraction grating 6ba by luminescence of the active layer 4) is
present around the hole 6b. The electric filed components of the
electric field around the hole 6b in the case of Mode B are
relatively large in a direction Dr1 intersecting with the
hypotenuse of the approximate right triangle of the bottom face 6c
(corresponding to the third side 6b3 shown in FIG. 3) and in a
direction Dr2 extending along this hypotenuse (corresponding to the
third side 6b3 shown in FIG. 3).
[0080] According to Non Patent Literature 2, the laser beam
generated by the electromagnetic field in Mode B has the
polarization component with the polarization angle=45.degree. which
is larger than the polarization components with the other
polarization angles. The polarization component with the
polarization angle=45.degree. is a polarization component in a
direction extending with an inclination of 45.degree. from the
x-axis and the y-axis, in the positive domain of x and the positive
domain of y and in the negative domain of x and the negative domain
of y.
[0081] Four light bands (Band A, Band B, Band C, and Band D) shown
in FIG. 18 are generated from the diffraction grating 6ba. The
laser beam generated by the electromagnetic field in Mode B
corresponds to the band edge of the light band in Band B shown in
FIG. 18.
[0082] FIG. 6 shows an example of calculation for the approximate
right triangle of the bottom face 6c of the hole 6b of the
diffraction grating layer 6 with the angle .PHI.=0.degree., the
aspect ratio=1, the roundedness=0.20.times.a, the filling
factor=20%, and the depth of the hole 6b=200 nm. The calculation
result shown in FIG. 6 was obtained on the assumption that the
material of the diffraction grating layer 6 was GaAs. The following
will describe the fact that the laser beam L1 of the semiconductor
laser element 1 is generated mainly by the electromagnetic field in
Mode B, with reference to FIG. 6. FIG. 6 shows four types of
magnetic field distributions generated by the diffraction grating
6ba and radiation coefficients (cm.sup.-1) corresponding to the
respective magnetic field distributions. A radiation coefficient is
light leakage (or light output) in the direction perpendicular to
the plane in each of Mode A to Mode D. The definition of the
radiation coefficient is described in Non Patent Literature 1. The
magnetic field distribution R9 corresponds to Mode B, the magnetic
field distribution R10 to Mode A, the magnetic field distribution
R11 to Mode C, and the magnetic field distribution R12 to Mode D.
In the case of the magnetic field distribution R9, the radiation
coefficient is the smallest, compared to the other magnetic field
distributions. Therefore, in the laser beam L1 of the semiconductor
laser element 1, the components generated by the electromagnetic
field with oscillation in the magnetic field distribution R9 (Mode
B) are more than the components generated by the respective
electromagnetic fields with the magnetic field distribution R10
(Mode A), the magnetic field distribution R11 (Mode C), and the
magnetic field distribution R12 (Mode D).
[0083] FIGS. 7 to 12 show shapes with which the magnetic field
distribution with the smallest radiation coefficient corresponds to
Mode B, as the result of calculation of the radiation coefficients
in a plurality of variations of the shape of the diffraction
grating 6ba. The material of the diffraction grating 6ba giving the
calculation results of FIGS. 7 to 12 is GaAs and the depth of the
holes 6b in the diffraction grating 6ba giving the calculation
results of FIGS. 7 to 12 is 200 nm. The calculation of the
radiation coefficients was carried out by use of the three
dimensional coupled-wave analysis of infinite periodic structure
shown in Non Patent Literature 1 and the shape of the diffraction
grating 6ba was defined by the aspect ratio (K2), angle .PHI.,
roundedness (K1), and filling factor (K3). In FIGS. 7 to 12, in the
cases of the shapes of hatched portions (hatched portions N1), the
magnetic field distribution with the smallest radiation coefficient
corresponds to Mode B. FIG. 7 is the calculation results in the
cases where the angle .PHI. is 0.degree.. FIG. 8 is the calculation
results in the cases where the angle .PHI. is 15.degree.. FIG. 9 is
the calculation results in the cases where the angle .PHI. is
30.degree.. FIG. 10 is the calculation results in the cases where
the angle .PHI. is 45.degree.. FIG. 11 is the calculation results
in the cases where the angle .PHI. is 60.degree.. FIG. 12 is the
calculation results in the cases where the angle .PHI. is
75.degree..
[0084] The semiconductor laser element 1 according to the
embodiment outputs the laser beam L1 through the diffraction
grating 6ba of the diffraction grating layer 6. The diffraction
grating 6ba has the plurality of holes 6b (lattice points) of the
approximate right triangle arranged along the square lattice R3. In
the case of the electromagnetic field mode (Mode B) at the second
band edge B from the low frequency side near the second .GAMMA.
point of the square lattice R3, the node R8 of the electromagnetic
field generated in the diffraction grating 6ba by luminescence of
the active layer 4 is located approximately at the same position as
the centroid of the approximate right triangle of the hole 6b and
the extrema of intensity of the magnetic field in the
electromagnetic field on the square lattice R3 are present around
the hole. It was discovered by Inventor's intensive and extensive
research that the beam quality of index M.sup.2<1 could be
achieved in the case of this Mode B. Therefore, the laser beam L1
output from the semiconductor laser element 1 according to the
embodiment has the beam quality of the index M.sup.2<1. The
value of this index M.sup.2 as beam quality is an excellent value
not more than one tenth of the values of the index M.sup.2 of
ordinary broad stripe edge emitting semiconductor lasers and VCSEL
(Vertical Cavity Surface Emitting LASER) for high output, enabling
reduction in converging radius. Therefore, the semiconductor laser
element 1 has a potential of realization of high energy
density.
[0085] The shape of the opening of the hole 6b as a lattice point
is the approximate right triangle. Each of the three vertices
(vertex 6b4, vertex 6b5, and vertex 6b6) of the approximate right
triangle of the opening of the hole 6b is rounded so as to overlap
the circumference of the reference circle Ci tangent at each
vertex. It was discovered by Inventor's intensive and extensive
research that the beam quality of the index M.sup.2<1 could be
maintained even if the vertex 6b4, vertex 6b5, and vertex 6b6 were
rounded.
[0086] The opening of the hole 6b as a lattice point has the first
side 6b1 and the second side 6b2. The first side 6b1 and the second
side 6b2 make a right angle. The first side 6b1 is inclined
relative to the lattice vector VX of the square lattice. In a
process of forming the laminate on the diffraction grating layer 6
by the regrowth method of the MOCVD process, the crystal quality of
the upper laminate varies depending upon the inclination angle of
the approximate right triangle (the angle of inclination relative
to the lattice vector). It was discovered by Inventor's intensive
and extensive research that the beam quality of the index M.sup.2
could be maintained because the oscillation at the band edge B was
possible even if the approximate right triangle of the lattice
point was inclined relative to the lattice vector. In the steps of
manufacturing the semiconductor laser element 1, where the
diffraction grating layer 6 and the laminate subsequent thereto are
formed by regrowth of the MOCVD process, the quality of the
laminate can be optimized by the foregoing inclination, depending
upon the shape of the lattice point.
[0087] The semiconductor laminate 1a in the semiconductor laser
element 1 according to the embodiment can be manufactured using the
III-V semiconductors containing GaAs. Since the manufacturing
technology has been established for such material system, the
manufacture of the semiconductor laser element 1 becomes relatively
easier.
[0088] In the semiconductor laser element 1 according to the
embodiment, the semiconductor laminate 1a further has the electron
blocking layer 5 and the electron blocking layer 5 lies between the
p-type cladding layer 7 and the active layer 4. The electron
blocking layer 5 enables capability for high output. As a similar
structure, it is possible to further use a hole blocking layer in
combination between the layer with the conductivity type of n-type
including the n-type cladding layer 3, and the active layer 4.
[0089] In the semiconductor laser element 1 according to the
embodiment, the diffraction grating layer 6 lies between the p-type
cladding layer 7 and the active layer 4. When the semiconductor
laminate 1a is formed from the n-side layer, the diffraction
grating layer 6 is formed after formation of the active layer 4
and, for this reason, the active layer 4 is prevented from being
directly damaged in a process of processing the diffraction grating
layer 6, whereby degradation of the active layer can be
avoided.
[0090] A method for manufacturing the semiconductor laser element 1
will be described with reference to FIGS. 13 and 14. Steps from
step S1 to step S11 are successively carried out, thereby
manufacturing a substrate product having the configuration of the
semiconductor laser element 1. In step S1, a first epitaxial layer
structure 20 is grown by the MOCVD process. The layer structure of
the first epitaxial layer structure 20 is shown in part (A) of FIG.
14. The first epitaxial layer structure 20 has n-GaAs Substrate
20a, n-AlGaAs Cladding layer 20b, i-AlGaAs Guide layer 20c,
i-InGaAs/AlGaAs 3QWs 20d, i-AlGaAs Carrier blocking layer 20e,
i-AlGaAs Guide layer 20f, and i-GaAs Guide layer 20g. The n-GaAs
Substrate 20a corresponds to the support substrate 2. The n-AlGaAs
Cladding layer 20b corresponds to the n-type cladding layer 3. A
layer consisting of the i-AlGaAs Guide layer 20c and
i-InGaAs/AlGaAs 3QWs 20d corresponds to the active layer 4. A layer
consisting of the i-AlGaAs Carrier blocking layer 20e and i-AlGaAs
Guide layer 20f corresponds to the electron blocking layer 5. The
i-GaAs Guide layer 20g is a layer where the diffraction grating 6ba
is formed. A surface 201 of the first epitaxial layer structure 20
is a surface of the i-GaAs Guide layer 20g. The surface 201
corresponds to the p-side surface 6a.
[0091] In step S2, a resist 21 is applied onto the surface 201 of
the first epitaxial layer structure 20. In step S3, a photonic
crystal pattern 22a is exposed on the resist 21 by use of electron
beam lithography exposure and the resist is developed with a liquid
developer. By this development, the resist 21 turns into a resist
22. The resist 22 has the photonic crystal pattern 22a.
[0092] In step S4, dry etching is carried out to transfer a
photonic crystal pattern 23a to the i-GaAs Guide layer 20g at the
surface 201 of the first epitaxial layer structure 20 from the
surface 201 side. By this transfer, the first epitaxial layer
structure 20 turns into a second epitaxial layer structure 23. The
second epitaxial layer structure 23 has the photonic crystal
pattern 23a. The surface where the photonic crystal pattern 23a is
formed in the second epitaxial layer structure 23 corresponds to
the p-side surface 6a shown in FIG. 1. The photonic crystal pattern
23a and the photonic crystal pattern 22a are the same pattern when
viewed from the direction (z-axis direction) perpendicular to the
surface 201. The depth of the photonic crystal pattern 23a can be
approximately from 100 to 300 nm from the surface 201 when the
thickness of the i-GaAs Guide layer 20g is, for example, about 300
nm; e.g., the depth can be about 100 nm from the surface 201, about
200 nm from the surface 201, or about 300 nm from the surface 201.
Through step S4, the i-GaAs Guide layer 20g turns into a layer
consisting of the i-GaAs Guide layer not including the photonic
crystal pattern 23a and the i-GaAs Guide layer including the
photonic crystal pattern 23a. Through step S4, the first epitaxial
layer structure 20 turns into the second epitaxial layer structure
23. The first epitaxial layer structure 20 has the i-GaAs Guide
layer 20g, whereas the second epitaxial layer structure 23 has the
layer consisting of the i-GaAs Guide layer not including the
photonic crystal pattern 23a and the i-GaAs Guide layer including
the photonic crystal pattern 23a, without the i-GaAs Guide layer
20g. Only this difference is the difference between the first
epitaxial layer structure 20 and the second epitaxial layer
structure 23. After step S4, step S5 is performed to remove the
resist 22 from the second epitaxial layer structure 23.
[0093] In step S6, a common pretreatment is carried out and
thereafter a fourth epitaxial layer structure 24 shown in part (B)
of FIG. 14 is grown by the MOCVD process. The fourth epitaxial
layer structure 24 has p-AlGaAs Cladding layer 24a and p-GaAs
Contact layer 24b. The p-AlGaAs Cladding layer 24a grows on the
surface of the i-GaAs Guide layer of the second epitaxial layer
structure 23 (the surface where the photonic crystal pattern 23a is
formed). In the step of growing the p-AlGaAs Cladding layer 24a,
AlGaAs adheres to the photonic crystal pattern 23a. The i-GaAs
Guide layer including the photonic crystal pattern 23a included in
the second epitaxial layer structure 23 turns into i-GaAs/AlGaAs PC
layer 20i containing Al (corresponding to the diffraction grating
6ba), with growth of the p-AlGaAs Cladding layer 24a. At this time,
hollow spaces (corresponding to the holes 6b) are formed inside the
i-GaAs/AlGaAs PC layer 20i. The photonic crystal pattern 23a of the
second epitaxial layer structure 23 turns into a photonic crystal
pattern 23a1 including AlGaAs and the hollow spaces (corresponding
to the holes 6b), with growth of the p-AlGaAs Cladding layer 24a.
The i-GaAs/AlGaAs PC layer 20i is a layer including the photonic
crystal pattern 23a1. In the end, the i-GaAs Guide layer 20g of the
first epitaxial layer structure 20 turns into the layer consisting
of the i-GaAs Guide layer 20h and i-GaAs/AlGaAs PC layer 20i,
through the transfer of the photonic crystal pattern 23a and the
growth of the p-AlGaAs Cladding layer 24a, and the first epitaxial
layer structure 20 turns via the second epitaxial layer structure
23 into a third epitaxial layer structure 231. The first epitaxial
layer structure 20 has the i-GaAs Guide layer 20g, whereas the
third epitaxial layer structure 231 has the layer consisting of the
i-GaAs Guide layer 20h and the i-GaAs/AlGaAs PC layer 20i, without
the i-GaAs Guide layer 20g. Only this difference is the difference
between the first epitaxial layer structure 20 and the third
epitaxial layer structure 231. The layer consisting of the i-GaAs
Guide layer 20h and the i-GaAs/AlGaAs PC layer 20i corresponds to
the diffraction grating layer 6. The steps up to step S6 result in
forming the whole of the epitaxial layer structure of PCSEL
(corresponding to the semiconductor laminate 1a of the
semiconductor laser element 1).
[0094] In step S7, an SiN layer 25 is formed on the surface of the
fourth epitaxial layer structure 24 (corresponding to the front
surface 1a1).
[0095] In step S8, using the ordinary exposure development
technology and Reactive Ion Etching (RIB), an opening 26a is formed
in a shape corresponding to the p-side electrode 27 (square shape
of 200 .mu.m square), in the SiN layer 25. By forming the opening
26a, the SiN layer 25 turns into an SiN layer 26. The SiN layer 26
has the opening 26a. In the opening 26a, the surface of the fourth
epitaxial layer structure 24 is exposed.
[0096] In step S9, a p-side electrode 27 is formed over the opening
26a by lift-off. The p-side electrode 27 is in contact with the
p-GaAs Contact layer 24b of the fourth epitaxial layer structure
24, through the opening 26a. The p-side electrode 27 corresponds to
the p-side electrode 10.
[0097] A material of the p-side electrode 27 to be used can be a
material for the electrodes provided on the semiconductor layers of
GaAs-based materials. The material of the p-side electrode 27 can
be, for example, a metal such as Au, Ti, Pt, or Cr. The p-side
electrode 27 can be, for example, Ti/Pt/Au, Ti/Au, Cr/Au, or the
like in order from the GaAs semiconductor layer side. The p-GaAs
Contact layer 24b in contact with the p-side electrode 27 is doped
with an impurity in a high concentration of not less than
1.times.10.sup.19/cm.sup.-3.
[0098] In step S10, the back surface of the third epitaxial layer
structure 231 (corresponding to the back surface 1a2) is polished
and an SiN layer 28 is formed at a location (location immediately
below the p-side electrode 27) on the back surface (corresponding
to the back surface 1a2) after polished, by use of the exposure
development technology. The SiN layer 28 also has a function as an
anti-reflection coat. An optical film thickness of the SiN layer 28
is .lamda./4 (.lamda. is the oscillation wavelength) of the
oscillation wavelength of the semiconductor laser element 1. The
SiN layer 28 has an opening 28a. In the opening 28a, the back
surface of the third epitaxial layer structure 231 is exposed.
[0099] In step S11, an n-side electrode 29 is formed by lift-off.
The n-side electrode 29 has a shape surrounding a surface emission
region on the back surface of the third epitaxial layer structure
231. The n-side electrode 29 corresponds to the n-side electrode
9.
[0100] A material of the n-side electrode 29 to be used can be a
material for the electrodes provided on the semiconductor layers of
GaAs-based materials. The material of the n-side electrode 29 can
be, for example, a mixture of a metal such as Au with a
semiconductor such as Ge. The n-side electrode can be, for example,
AuGe, AuGe/Au, or the like.
[0101] After completion of execution of the steps from step S1 to
step S11 described above, the substrate product having the
configuration of the semiconductor laser element 1 is manufactured.
After step S11, the substrate product manufactured by the steps up
to step S11 is divided into chips of a plurality of semiconductor
laser elements 1.
[0102] Example of the semiconductor laser element 1 will be
described with reference to FIGS. 15 to 22. FIGS. 15 to 17 are
drawings for explaining the beam quality of Example of the
semiconductor laser element 1. First, the beam radius W of the
laser beam L1 of Example was measured. The electric current
injected into Example was approximately 500 mA. Each of a plurality
of marks R13a1 indicates a measurement of the beam radius W (mm) in
the x-axis direction. Each of a plurality of marks R13b1 indicates
a measurement of the beam radius W (mm) in the y-axis direction. A
curve R13a2 is a curve obtained by fitting to the measurements of
the beam radius W in the x-axis direction. A curve R13b2 is a curve
obtained by fitting to the measurements of the beam radius W in the
y-axis direction. In the laser beam L1 of Example, the beam waist
R13 corresponds to the beam waist R4 in FIG. 4. The measurement
results R14 in FIG. 16 indicate the result of calculation of the
index M.sup.2 in the x-axis direction using the curve R13a2 and the
result of calculation of the index M.sup.2 in the y-axis direction
using the curve R13b2. Each mark R14a in FIG. 16 indicates the
index M.sup.2 in the x-axis direction. Each mark R14b in FIG. 16
indicates the index M.sup.2 in the y-axis direction.
[0103] The injected current into Example was set not only at 500 mA
but also at 300 mA, 400 mA, and 600 mA; the same measurement as in
FIG. 15 was performed using each of the injected currents; the
index M.sup.2 in the x-axis direction and the index M.sup.2 in the
y-axis direction were calculated at each of the injected currents;
the calculation results are shown in FIG. 16. Numerals
corresponding to the results shown in the graph of FIG. 16 are
shown in FIG. 17. As shown in FIGS. 16 and 17, it is seen that the
index M.sup.2 in the x-axis direction and the index M.sup.2 in the
y-axis direction are smaller than 1, particularly, at the injected
currents of 400 mA, 500 mA, and 600 mA. When the injected current
is 300 mA, the index M.sup.2 in the y-axis direction is smaller
than 1. When the injected current is 300 mA, the index M.sup.2 in
the x-axis direction is larger than 1 but almost close to 1, a
relatively small value.
[0104] Part (A) of FIG. 18 shows the result of imaging of photonic
bands immediately before oscillation of Example of the
semiconductor laser element 1 and part (B) of FIG. 18 an
oscillation spectrum immediately after oscillation of the laser
beam L1 of Example. The unit of wave number on the horizontal axis
in part (A) of FIG. 18 is 2.pi./a (a is the value of the lattice
constant a of the square lattice R3) and the unit of frequency on
the vertical axis in part (A) of FIG. 18 is c/a (c is the speed of
light in vacuum; a is the value of the lattice constant a of the
square lattice R3). The photonic bands near the second .GAMMA.
point of the semiconductor laser element 1 are four types, Band A,
Band B, Band C, and Band D. The wave vector of .GAMMA.-X
corresponds to the x-axis direction. The wave vector of .GAMMA.-M
corresponds to the direction extending at 45.degree. to the x-axis
and the y-axis. It is understood that the laser beam L1 is
oscillated at the band edge B, by correspondence between the
oscillation spectrum immediately after the oscillation of the laser
beam L1 shown in part (B) of FIG. 18 and the photonic band
immediately before the oscillation shown in part (A) of FIG. 18.
The imaging result of the light bands shown in FIG. 18 were
obtained by injecting the electric current of 0.98.times.Ith into
Example, where the threshold current Ith is equal to 190 mA, in the
environment of 25.degree. C., so as to implement continuous
oscillation of Example. The measurement result of the intensity
spectrum shown in FIG. 18 was obtained by injecting the electric
current of 1.03.times.Ith into Example in the environment of
25.degree. C., so as to implement continuous oscillation of
Example.
[0105] FIG. 19 shows the results of measurement of beam intensity
of the laser beam L1 from Example of the semiconductor laser
element 1, for each of four types of polarization components (or
for each of four types of polarization angles). The measurement
result R15 is the result of measurement of beam intensity of the
polarization component with the polarization angle=0.degree. of the
laser beam L1, in the range of the beam divergence angle .theta. of
1.5.degree.. The polarization component with the polarization
angle=0.degree. is the polarization component in the x-axis
direction. The measurement result R16 is the result of measurement
of beam intensity of the polarization component with the
polarization angle=45.degree. of the laser beam L1, in the range of
the beam divergence angle .THETA. of 1.5.degree.. The polarization
component with the polarization angle=45.degree. is the
polarization component in the direction extending at the
inclination of 45.degree. from the x-axis and the y-axis, in the
positive x domain and positive y domain and in the negative x
domain and negative y domain. The measurement result R17 is the
result of measurement of beam intensity of the polarization
component with the polarization angle=90.degree. of the laser beam
L1, in the range of the beam divergence angle .THETA. of
1.5.degree.. The polarization component with the polarization
angle=90.degree. is the polarization component in the y-axis
direction. The measurement result R18 is the result of measurement
of beam intensity of the polarization component with the
polarization angle=135.degree. of the laser beam L1, in the range
of the beam divergence angle .THETA. of 1.5.degree.. The
polarization component with the polarization angle=135.degree. is
the polarization component in the direction extending at the
inclination of 45.degree. from the x-axis and the y-axis, in the
positive x domain and negative y domain and in the negative x
domain and positive y domain. The measurement result R15 to the
measurement result R18 were obtained by injecting the electric
current of about 500 mA into Example in the environment of
25.degree. C. to implement continuous oscillation of Example.
[0106] The injected current into Example was set at 300 mA, 400 mA,
and 600 mA, in addition to 500 mA, the same measurement as in FIG.
19 was carried out by use of each of the injected currents, and
rates of beam intensity for the respective polarization components
were calculated at each of the injected currents; the calculation
results are shown in FIG. 20. The horizontal axis of FIG. 20
represents the polarization angle (.degree.). The vertical axis of
FIG. 20 represents the rate (%) of beam intensity. Each mark R19
indicates the measurement result obtained by the injected current
of 300 mA, each mark R20 the measurement result obtained by the
injected current of 400 mA, each mark R21 the measurement result
obtained by the injected current of 500 mA, and each mark R22 the
measurement result obtained by the injected current of 600 mA. The
rate of beam intensity for each polarization component refers to a
rate (%) of the beam intensity of each polarization component to
the whole beam intensity. The beam intensities were measured in the
range of the beam divergence angle .THETA. of 1.5.degree.. With
reference to FIG. 20, the beam intensities of the polarization
component with the polarization angle=45.degree. are the largest,
compared to the polarization components with the other polarization
angles, in the laser beam L1 of Example. The components generated
by the electromagnetic field in Mode B shown in part (B) of FIG. 5
include a larger part of the polarization component with the
polarization angle=45.degree., than the other polarization
components (Non Patent Literature 2). Therefore, it is seen that
the laser beam L1 of Example is one generated by the
electromagnetic field in Mode B.
[0107] With reference to FIGS. 18 to 20, it is understood that the
laser beam L1 of Example of the semiconductor laser element 1
mainly includes the components generated by the electromagnetic
field in Mode B shown in part (B) of FIG. 5. It is seen that the
components generated by the electromagnetic field in Mode B realize
the index M.sup.2 smaller than 1.
[0108] FIG. 21 shows an intensity spectrum of the laser beam L1 in
Example of the semiconductor laser element 1. The horizontal axis
of FIG. 21 represents the wavelength (nm) and the vertical axis the
beam intensity (dB). It is seen with reference to FIG. 21 that the
laser beam L1 has a peak R23 in the wavelength range from 962 nm to
963 nm. Therefore, the laser beam L1 is found to be a single
mode.
[0109] FIG. 22 shows SEM (Scanning Electron Microscope) images in
the manufacturing process of Example of the semiconductor laser
element 1. The SEM images shown in FIG. 22 are SEM images of the
photonic crystal pattern corresponding to the photonic crystal
pattern 23a at the stage of step S5 in FIG. 13. The SEM image in
part (A) of FIG. 22 is an image of the pattern viewed from the
opposite side to the n-GaAs Substrate 20a, and the SEM image in
part (B) of FIG. 22 an image of the photonic crystal pattern 23a
viewed from the orientation flat side of the substrate product
consisting of the second epitaxial layer structure 23. The lattice
constant a of the photonic crystal pattern 23a in the SEM images of
FIG. 22 is 290 nm.
[0110] FIG. 23 show shapes of the unit lattice R3a with the aspect
ratios (1.00, 1.06, 1.12, and 1.20) including the aspect ratio
(1.0) in part (A) of FIG. 7. In all the shapes of the unit lattice
R3a shown in FIG. 23, the filling factor of the hole 6b is 20(%)
and the angle .PHI. the same (0.degree.) as the angle .PHI. of the
shape shown in FIG. 7.
[0111] FIG. 24 shows correlations between the radiation coefficient
(cm.sup.-1) and filling factor in each of the four types of
electromagnetic field modes (Modes A, B, C, and D), for the
respective shapes of the unit lattice R3a shown in FIG. 23. Graph
R25a corresponds to Mode A, graph R25b to Mode B, graph R25c to
Mode C, and graph R25d to Mode D. In the device structure shown in
FIG. 1, when the lengths in the x-direction and y-direction of the
photonic crystal structure are set to sufficiently large values,
light leakage into the x-direction and y-direction not contributing
to optical output can be kept sufficiently small. In the
simulations shown in the present embodiment, an ideal state is
considered to be a case where the lengths in the x-direction and
y-direction are infinite. In this case, the light leakage into the
x-direction and y-direction is zero and, the light leakage into the
z-direction or the radiation coefficient coincides with the light
leakage into all directions or threshold gain. Therefore, the
radiation coefficient difference will be referred to hereinafter as
threshold gain difference.
[0112] The electromagnetic field mode used in the present
embodiment is Mode B as described above, out of the four types of
electromagnetic field modes (Modes A, B, C, and D). When the
threshold gain of Mode B is the lowest among the four types of
electromagnetic field modes, oscillation in Mode B can be expected.
It is seen from the simulation results of the threshold gains shown
in FIG. 24 that the electromagnetic field mode with the next lowest
threshold gain to Mode B is Mode A, in all the cases where Mode B
has the lowest threshold gain among the four types of
electromagnetic field modes. In the simulation results of threshold
gains shown in FIG. 24, stabler oscillation can be expected as the
threshold gain difference between Mode B and Mode A becomes
larger.
[0113] FIG. 25 shows the simulation results of threshold gain
difference between Mode A and Mode B. In FIG. 25, dark colored
portions indicate ranges where the threshold gain difference is
large (i.e., where stabler oscillation can be expected), and light
colored portions indicate portions where the threshold gain
difference is small. As shown in FIG. 25, the threshold gain
difference between Mode A and Mode B demonstrates monotonic
variation. Particularly, the threshold gain difference is the
largest with the unit lattice R3a of the shape with the filling
factor of 15 to 20%, the aspect ratio of 1.00, and the roundedness
of 0.00.times.a (a is the lattice constant) and, with variation
from this shape, the threshold gain difference between Mode A and
Mode B monotonically decreases. In portions without data points in
FIG. 25, the difference is considered to vary continuously from the
data points in FIG. 25, because of the physical background
described below.
[0114] The simulation results shown in respective drawings of FIGS.
26 to 36 show correlations of threshold gain differences with
values of the filling factor and values of the roundedness with the
aspect ratio being kept constant, out of the three factors to
define the shape of the unit lattice R3a (which are the
roundedness, the filling factor, and the aspect ratio, while the
angle .PHI. is zero degree). FIG. 26 shows the case of the aspect
ratio=1.00, FIG. 27 the case of the aspect ratio=1.02, FIG. 28 the
case of the aspect ratio=1.04, FIG. 29 the case of the aspect
ratio=1.06, FIG. 30 the case of the aspect ratio=1.08, FIG. 31 the
case of the aspect ratio=1.10, FIG. 32 the case of the aspect
ratio=1.12, FIG. 33 the case of the aspect ratio=1.14, FIG. 34 the
case of the aspect ratio=1.16, FIG. 35 the case of the aspect
ratio=1.18, and FIG. 36 the case of the aspect ratio=1.20. The
simulation results shown in respective drawings of FIGS. 37 to 41
show correlations of threshold gain differences with values of the
filling factor and values of the aspect ratio with the roundedness
being kept constant, out of the three factors to define the shape
of the unit lattice R3a (which are the roundedness, the filling
factor, and the aspect ratio, while the angle .PHI. is zero
degree). FIG. 37 shows the case of the roundedness=0.00.times.a,
FIG. 38 the case of the roundedness=0.05.times.a, FIG. 39 the case
of the roundedness=0.10.times.a, FIG. 40 the case of the
roundedness=0.15.times.a, and FIG. 41 the case of the
roundedness=0.20.times.a.
[0115] The Inventor discovered in view of FIGS. 37 to 41 that the
oscillation in Mode B became particularly prominent when the shape
of the approximate right triangle of the bottom face 6c of the hole
6b satisfies any one of the following conditions (1) to (10):
[0116] (1) the roundedness (K1 which is the same for the
description hereinafter) is 0.00.times.the lattice constant (the
lattice constant might be represented by a in the above
description, which is the same for the description hereinafter),
the filling factor (K3 which is the same for the description
hereinafter) is not less than 10% and not more than 25%, and the
aspect ratio (K2 which is the same for the description hereinafter)
is not less than 1.00 and not more than 1.16;
[0117] (2) the roundedness is 0.00.times.the lattice constant, the
filling factor is not less than 15% and not more than 25%, and the
aspect ratio is not less than 1.16 and not more than 1.20;
[0118] (3) the roundedness is 0.05.times.the lattice constant, the
filling factor is not less than 9% and not more than 24%, and the
aspect ratio is not less than 1.00 and not more than 1.20; [0119]
(4) the roundedness is 0.10.times.the lattice constant, the filling
factor is not less than 10% and not more than 22%, and the aspect
ratio is not less than 1.00 and not more than 1.08;
[0120] (5) the roundedness is 0.10.times.the lattice constant, the
filling factor is not less than 10% and not more than 21%, and the
aspect ratio is not less than 1.08 and not more than 1.12; [0121]
(6) the roundedness is 0.10.times.the lattice constant, the filling
factor is not less than 10% and not more than 18%, and the aspect
ratio is not less than 1.12 and not more than 1.20;
[0122] (7) the roundedness is 0.15.times.the lattice constant, the
filling factor is not less than 11% and not more than 22%, and the
aspect ratio is not less than 1.00 and not more than 1.08;
[0123] (8) the roundedness is 0.15.times.the lattice constant, the
filling factor is not less than 11% and not more than 21%, and the
aspect ratio is not less than 1.08 and not more than 1.16;
[0124] (9) the roundedness is 0.15.times.the lattice constant, the
filling factor is not less than 11% and not more than 20%, and the
aspect ratio is not less than 1.16 and not more than 1.20;
[0125] (10) the roundedness is 0.20.times.the lattice constant, the
filling factor is not less than 13% and not more than 22%, and the
aspect ratio is not less than 1.00 and not more than 1.20.
[0126] It is noted that the aspect ratios (K2) in the above
conditions (1) to (10) can be either h/b or b/h of the hole 6b of
the unit lattice R3a shown in FIG. 3 as long as it is common to all
the unit lattices R3a of the diffraction grating 6ba.
[0127] The below will describe continuity between the
discretely-obtained simulation results shown in FIGS. 24 to 41,
from the physical viewpoint. The threshold gains of the simulation
results shown in FIGS. 24 to 41 correspond to likeliness of leakage
of light from the cavity composed of the p-type cladding layer 7,
the diffraction grating layer 6 with the photonic crystal
structure, the electron blocking layer 5, the active layer 4, and
the n-type cladding layer 3. Namely, the threshold gain increases
as light is more likely to leak. The simulations shown in FIGS. 24
to 41 are those obtained on the premise that the size of the
photonic crystal structure of the diffraction grating layer 6 is
infinite in the lateral directions (directions in which the
photonic crystal structure of the diffraction grating layer 6
extends, or directions perpendicular to the direction of emission
of the laser beam L1) and that there occurs no light leakage in the
lateral directions. The factor to determine the magnitude of the
threshold gain is only the light leakage in the direction
perpendicular to the surface of the diffraction grating layer 6 (or
in the direction perpendicular to the foregoing lateral
directions), i.e., light leakage in the emission direction of the
laser beam L1. The magnitude of the light leakage in the case where
there is the light leakage in the emission direction of the laser
beam L1 in this manner, varies depending upon symmetry of the
electric field distribution in the photonic crystal plane. This
electric field distribution differs mode by mode and varies with
variation in shape of the hole. As apparent from the boundary
conditions of the Maxwell's equations in general, the magnitude of
the electric field crossing an interface between different
refractive indices varies depending upon the refractive indices
(cf. the description in Non Patent Literature 3). Since the
electric field in the structure of the diffraction grating layer 6
used for the simulations of FIGS. 24 to 41 has the components in
the directions parallel to the foregoing lateral directions, the
symmetry of the electric field varies with variation in the shape
of the unit lattice R3a (hole 6b) viewed from the direction
perpendicular to the lateral directions (or from the emission
direction of the laser beam L1). Incidentally, in the photonic
crystal lasers including the semiconductor laser element 1 of the
present embodiment, the resonant condition is formed in the
photonic crystal plane and light diffracted into the direction
perpendicular to the photonic crystal plane is utilized as output;
therefore, destructive interference of light occurs depending upon
the symmetry of the electric field in the photonic crystal plane,
so as to change the magnitude of the output in the direction
perpendicular to the photonic crystal plane. Therefore, with change
in the shape of the unit lattice R3a (hole 6b) as described above,
the symmetry of the electric field in the photonic crystal plane
varies, the magnitude of the destructive interference of the light
diffracted into the direction perpendicular to the photonic crystal
plane varies, and the light leakage into the direction
perpendicular to the photonic crystal plane varies; therefore, the
threshold gain also varies according to this variation. Since the
electric field distributions are different among the modes of Modes
A to D, the magnitudes of the threshold gains are also different
among the modes of Modes A to D. In the simulations of FIGS. 24 to
41 the discrete simulation results were obtained with discrete
variation in the shape of the unit lattice R3a (hole 6b), and it
can be contemplated from the above-described physical background
that the discrete results of FIGS. 24 to 41 are continuously
interpolated.
[0128] The principles of the present invention were illustrated and
described above in the preferred embodiment but a person skilled in
the art can recognize that the present invention can be modified in
arrangement and details without departing from the principles. The
present invention is by no means intended to be limited to the
specific configurations disclosed in the embodiment. Therefore, the
Inventor claims the right to all modifications and changes falling
within the scope of claims and coming from the scope of the spirit
thereof.
[0129] For example, in the case of the above embodiment, the
diffraction grating layer 6 lies between the active layer 4 and the
p-type cladding layer 7, but it may be provided between the active
layer 4 and the n-type cladding layer 3. In the case of this
arrangement, the electron blocking layer 5 also lies between the
active layer 4 and the p-type cladding layer 7.
INDUSTRIAL APPLICABILITY
[0130] The present invention is applicable to the semiconductor
laser elements required to have high beam quality (the index
M.sup.2<1).
REFERENCE SIGNS LIST
[0131] 1 . . . semiconductor laser element; 10 . . . p-side
electrode; 1a . . . semiconductor laminate; 1a1 . . . front
surface; 1a2 . . . back surface; 1b1, 1b2 . . . laminates; 2 . . .
support substrate; 20 . . . first epitaxial layer structure; 201 .
. . surface; 20a . . . n-GaAs Substrate; 20b . . . n-AlGaAs
Cladding layer; 20c . . . i-AlGaAs Guide layer; 20d . . .
i-InGaAs/AlGaAs 3QWs; 20e . . . i-AlGaAs Carrier blocking layer;
20f . . . i-AlGaAs Guide layer; 20g . . . i-GaAs Guide layer; 20h .
. . i-GaAs Guide layer; 20i . . . i-GaAs/AlGaAs PC layer; 21, 22 .
. . resists; 22a . . . photonic crystal pattern; 23 . . . second
epitaxial layer structure; 231 . . . third epitaxial layer
structure; 23a . . . photonic crystal pattern; 23a1 . . . photonic
crystal pattern; 24 . . . fourth epitaxial layer structure; 24a . .
. p-AlGaAs Cladding layer; 24b . . . p-GaAs Contact layer; 25, 26 .
. . SiN layers; 26a, 28a . . . openings; 27 . . . p-side electrode;
28 . . . SiN layer; 29 . . . n-side electrode; 2a . . . principal
surface; 3 . . . n-type cladding layer; 4 . . . active layer; 5 . .
. electron blocking layer; 6 . . . diffraction grating layer; 6a .
. . p-side surface; 6b . . . holes; 6b1 . . . first side; 6b2 . . .
second side; 6b3 . . . third side; 6b4, 6b5, 6b6 . . . vertices;
6ba . . . diffraction grating; 6c . . . bottom face; 7 . . . p-type
cladding layer; 8 . . . contact layer; 9 . . . n-side electrode; a
. . . lattice constant; b . . . side length; Ci . . . reference
circle; D . . . converging radius; d . . . converging radius; h . .
. side length; L1 . . . laser beam; L2 . . . lens; N1 . . . hatched
portions; M1 . . . magnetic field distribution; R1 . . . direction;
R10, R11, R12, R9 . . . magnetic field distributions; R13, R4 . . .
beam waists; R13a1, R13b1, R14a, R14b, R19, R20, R21, R22 . . .
marks (legends); R13a2, R13b2 . . . curves; R14, R15, R16, R17, R18
. . . measurement results; R2 . . . luminous region; R23 . . .
peak; R25a, R25b, R25c, R25d . . . graphs; R3 . . . square lattice;
R3a . . . unit lattice; R5, R6 . . . beam shapes; R7 . . .
directions of electric fields; R8 . . . node of electromagnetic
field; Ra . . . reference radius; S1, S10, S11, S2, S3, S4, S5, S6,
S7, S8, S9 . . . steps; VX, VY . . . lattice vectors; W . . . beam
radius; .THETA., .theta. . . . beam divergence angles; Dr1, Dr2 . .
. directions; .PHI. . . . angle.
* * * * *